Many electrical devices are designed to operate in conjunction with other electrical devices. For example, a charger device is designed to supply a specified voltage and/or electrical current to a battery operated electrical device in order to charge batteries of the battery operated electrical device. The battery operated electrical device can be, for example, a mobile phone or a palmtop computer. As another example, a data collecting and analysing device is designed to collect data from another electrical device when the data collecting and analysing device is connected to the other electrical device. The other electrical device can be, for example, an electronic control system of an engine of a car. An electrical device of the kind described above shall start to operate in a desired way as a response to a situation in which the electrical device is connected to another electrical device.
In a solution according to the prior art, an electrical device is kept in a full state of readiness when the electrical device is energized but the electrical device is not connected to another electrical device. For example, an output voltage of a charger device is kept in its specified value also when no other electrical device is connected to the charger device. For example, in charger devices for mobile phones there is typically a 100-300 mW power loss in a situation in which a charger device is connected to a power grid but it is not connected to a mobile phone. Therefore, keeping an electrical device in a full state of readiness may cause undesirable waste of energy. In charger devices comprising a switched mode power supply the above-mentioned power loss can be decreased to some extent by reducing a switching frequency of the switched mode power supply when the charger device is not loaded.
In another solution according to the prior art, an electrical device is equipped with a switch or with some other control means with the aid of which a user of the electrical device can switch the electrical device into an active operating mode e.g. after connecting the electrical device to another electrical device. The need to operate a switch or other control means makes, however, the usage of the electrical device more cumbersome and inconvenient. Furthermore, a risk for erroneous use is increased.
In light of the above-presented, there is a need for technical solutions that can be used for detecting a situation in which an electrical device that may be set in a low power state is connected to another electrical device.